Sinkhole and surface depression locations are shown on a map of Pennsylvania. Additional information on the local density of the karst features can be seen with a click of a data point. An explanation of the source of the karst data is also provided.

Sinkholes, along with caves, are a definitive part of Pennsylvania’s landscape we call karst. The chemical and physical processes that have helped to form this unique landscape have taken place over hundreds of millions of years.

Karst is common to areas underlain by carbonate bedrock (limestone and dolostone). These rocks are more easily dissolved than other rocks by a weak, naturally forming acid formed by the mixture of water and carbon dioxide. This dissolving process is enhanced along the many fractures found within the bedrock and over time has created a unique subsurface plumbing network.

Just as we have drains and pipes in our homes that help move water from one place to another, the karst system uses the widened fractures as drains and pipes in the carbonate bedrock to help convey water to the water table. Typically, the drains in the karst network are clogged with soil, but at times, water can act as a de-clogging agent and flush the karstic drains open creating a sinkhole.

The water-driven nature of karst systems lends them to be more sensitive to changes in land use. Rapid and widespread groundwater contamination or the sudden “unclogging” of a karst drain is a public safety as well as an economic concern.

When we consider how to manage stormwater runoff, infrastructure layout and design, and utilize groundwater as a resource, it becomes important to understand the relationships between activities at the surface and their potential impact beneath.